Inorganic Tin Compounds as Flame, Smoke, and Carbon Monoxide

Chapter 14

Inorganic Tin Compounds as Flame, Smoke, and Carbon Monoxide Suppressants for Synthetic Polymers Downloaded by UNIV OF CALIFORNIA SANTA BARBARA on June 15, 2016 | http://pubs.acs.org Publication Date: May 9, 1990 | doi: 10.1021/bk-1990-0425.ch014

1

2

P. A. Cusack and A. J. Killmeyer 1

International Tin Research Institute, Uxbridge, United Kingdom Tin Research Institute, Inc., Columbus, OH 43201 2

In view of the current demand for novel, non-toxic flame- and smoke-suppressant systems for synthetic polymers, certain inorganic tin compounds have been evaluated as fire retardants in a number of plastic and elastomeric substrates. The results obtained indicate that tin compound additives, in particular, zinc hydroxystannate and zinc stannate, exhibit beneficial properties both in halogenated and halogen-free formulations. The tin compounds appear to act predominantly in the condensed phase by a char -promoting mechanism, and this leads to a significant decrease in the amounts of smoke and toxic gases evolved during polymer combustion. The observed carbon monoxide-suppression is particularly interesting, since CO inhalation is now known to be the cause of death in the vast majority of fire fatalities.

The l a s t two decades have seen a major growth i n t h e use o f s y n t h e t i c polymers as m a t e r i a l s f o r c o n s t r u c t i o n , i n s u l a t i o n , p a c k a g i n g , u p h o l s t e r y and t r a n s p o r t a p p l i c a t i o n s (_1_). U n f o r t u n a t e l y , this p e r i o d has a l s o seen a d r a m a t i c i n c r e a s e i n t h e number o f s e r i o u s f i r e s , and t h e number o f deaths and i n j u r i e s i n f i r e s remains a p p a l l i n g l y high. F i r e deaths a r e n o r m a l l y v i o l e n t i n n a t u r e , and smoke i n h a l a t i o n and not f i r e i t s e l f i s t h e k i l l e r t h a t a c c o u n t s f o r over 80% o f f i r e deaths (2). T h e r e f o r e , r e c e n t advances i n f i r e t e s t i n g have p l a c e d g r e a t emphasis i n d e v e l o p i n g p r o d u c t s t h a t have low flame s p r e a d p r o p e r t i e s and a r e low smoke p r o d u c i n g . The use o f flame r e t a r d a n t s i n polymers has i n c r e a s e d d r a m a t i c a l l y i n r e c e n t y e a r s , i n p a r a l l e l t o t h e growth o f t h e p l a s t i c s i n d u s t r y (J_). Data f o r t h e U.S. consumption o f t h e s e c h e m i c a l s d u r i n g 1985 a r e p r e s e n t e d i n T a b l e I . Many o f t h e e x i s t i n g commercial a d d i t i v e s , however, have problems a s s o c i a t e d w i t h t h e i r use. In p a r t i c u l a r , c e r t a i n f l a m e - r e t a r d a n t systems a r e known t o cause an i n c r e a s e i n t h e amount o f smoke and t o x i c / c o r r o s i v e

0097-6156/90/0425-0189S06.50/0 © 1990 American Chemical Society

Nelson; Fire and Polymers ACS Symposium Series; American Chemical Society: Washington, DC, 1990.

190

FIRE A N D POLYMERS

gases g e n e r a t e d by p l a s t i c s i f they burn ( M . In a d d i t i o n , a number of the commercial f i r e r e t a r d a n t s have been found t o p o s s e s s u n d e s i r a b l e t o x i c o l o g i c a l p r o p e r t i e s themselves, ( 5 , 6 ) and t h e r e has been c o n s i d e r a b l e i n t e r e s t i n f i n d i n g new, s a f e r c h e m i c a l a d d i t i v e s f o r flammable m a t e r i a l s .

Downloaded by UNIV OF CALIFORNIA SANTA BARBARA on June 15, 2016 | http://pubs.acs.org Publication Date: May 9, 1990 | doi: 10.1021/bk-1990-0425.ch014

Table I. Flame R e t a r d a n t s f o r P l a s t i c s (USA Consumption, 1 9 8 5 ) Metric

Chemical ADDITIVES: Alumina t r i h y d r a t e Antimony o x i d e s Boron compounds Bromine compounds C h l o r i n e compounds Phosphorus compounds Others REACTIVES TOTAL =

tonnes

93,900 16,000 5,000 17,000 13,000 28,000 8,100 8,900 189,900

SOURCE: Data from the Fire Retardant Chemicals Association. Reproduced with permission from ref. 3. Copyright 1985 Modern Plastics. As a r e s u l t , s e v e r a l i n o r g a n i c compounds have found a p p l i c a t i o n i n t h i s f i e l d , and alumina t r i h y d r a t e , A 1 ( 0 H ) i s now by f a r the h i g h e s t volume flame r e t a r d a n t (3). I t s use, however, i s l i m i t e d t o those polymers which can t o l e r a t e the e x c e p t i o n a l l y h i g h l o a d i n g s r e q u i r e d t o be e f f e c t i v e , w i t h o u t s e r i o u s l y a f f e c t i n g the m e c h a n i c a l p r o p e r t i e s o f the s u b s t r a t e (]_). At the p r e s e n t time, i n o r g a n i c t i n compounds f i n d a r e l a t i v e l y s m a l l use i n n a t u r a l polymers, p a r t i c u l a r l y as f l a m e - r e s i s t t r e a t ments f o r w o o l l e n rugs and s h e e p s k i n s ( 8 , 9 ) . Although c e r t a i n other metal d e r i v a t i v e s have r e c e i v e d more a t t e n t i o n , t h e r e has been much i n t e r e s t r e c e n t l y i n the p o t e n t i a l use o f t i n c h e m i c a l s as flame r e t a r d a n t s and smoke s u p p r e s s a n t s f o r s y n t h e t i c polymers ( 1 0 ) . The purpose o f t h i s paper i s t o b r i e f l y r e v i e w r e c e n t r e s e a r c h i n t o the e f f e c t i v e n e s s and mode o f a c t i o n o f t i n compounds as f i r e r e t a r d a n t s i n a number o f h a l o g e n a t e d and h a l o g e n - f r e e , p l a s t i c and elastomeric substrates. TIN

ADDITIVES

Anhydrous t i n ( I V ) o x i d e ( ' S u p e r l i t e ' g r a d e ) and B - s t a n n i c a c i d ('Metastannic a c i d ' ) were s u p p l i e d by K e e l i n g & Walker L t d . , S t o k e on-Trent. ' 3 - s t a n n i c a c i d p a s t e ' was p r e p a r e d a t C h i n g h a l l L t d . , M i l t o n Keynes, by d i s p e r s i n g K e e l i n g & Walker's M e t a s t a n n i c a c i d , a t a l e v e l of 7 3 % i n a phthalate p l a s t i c i s e r . ' C o l l o i d a l t i n oxide', a 2 5 % aqueous d i s p e r s i o n o f SnO^, was s u p p l i e d by N y a c o l P r o d u c t s I n c . , Ashland, Mass., U.S.A. Z i n c h y d r o x y s t a n n a t e and z i n c s t a n n a t e were s y n t h e s i s e d a t I.T.R.I, a c c o r d i n g t o p r e v i o u s l y r e p o r t e d p r o c e d u r e s : ( 1 1 , 1 2 )


14.

CUSACK & KILLMEYER

Na Sn(OH) 2

ZnSn(OH), b

6

191

Inorganic Tin Compounds

+ ZnCl ^

H 2

2 ° ^ ZnSn(OH) | c

ZnSnO^ 3

+

+

2NaCl

3H 0 2 o

The i d e n t i t i e s of the p r o d u c t s were c o n f i r m e d by i n f r a r e d s p e c t r o s c o p y and x - r a y powder d i f f r a c t i o n p a t t e r n s . P h y s i c a l data on the i n o r g a n i c t i n a d d i t i v e s s t u d i e d a r e g i v e n i n T a b l e II.


TEST METHODS Flammability. F l a m m a b i l i t y of the samples, i n the form o f t h i n s t r i p s o f approximate dimensions o f 120mm x 7mm x 3mm was determined by measurement o f t h e i r oxygen i n d i c e s ( 0 1 ' s ) a c c o r d i n g to ASTM D2863, u s i n g a S t a n t o n - R e d c r o f t FTA module. I t has been e s t a b l i s h e d t h a t the 01 v a l u e s o f polymers f a l l , :.n some c a s e s d r a m a t i c a l l y , when the s u r r o u n d i n g gas m i x t u r e i s heated (J_). C o n s e q u e n t l y , the 01 t e s t has been extended to m a t e r i a l s at e l e v a t e d t e m p e r a t u r e s , and the h i g h temperature 0 1 s o f polymer samples were determined u s i n g a S t a n t o n - R e d c r o f t HFTA i n s t r u m e n t . The temperature index (TI) o f a polymer i s d e f i n e d as the temperature at which the t e s t specimen j u s t s u p p o r t s combustion i n a i r . f

Smoke d e n s i t y . O p t i c a l d e n s i t y measurements on the smoke e v o l v e d from b u r n i n g p l a s t i c samples were c a r r i e d out u s i n g an NBS Smoke Chamber. The samples, which measured 75mm x 75mm, w i t h a t h i c k n e s s o f 0.6 - 4mm, were burned i n the ' f l a m i n g mode i n a c c o r d a n c e w i t h ASTM E662-79. S p e c i f i c smoke d e n s i t y (Ds) v a l u e s r e p o r t e d are the averages o f t h r e e independent d e t e r m i n a t i o n s . 1

Carbon Monoxide E v o l u t i o n . D e t e r m i n a t i o n of the carbon monoxide e v o l v e d d u r i n g combustion o f polymer samples i n NBS Chamber experiments was c a r r i e d out u s i n g a T e l e g a n CO Sensor (Type 3 F ) . Quoted v a l u e s are the n u m e r i c a l averages o f t h r e e independant determinations. HALOGEN-CONTAINING POLYMER SYSTEMS The f l a m e - r e t a r d a n t a c t i o n of c h l o r i n e and bromine compounds, e i t h e r as p h y s i c a l l y - i n c o r p o r a t e d a d d i t i v e s to an o r g a n i c polymer or as p a r t of the polymer s t r u c t u r e i t s e l f , i s w e l l e s t a b l i s h e d (J_). Indeed, h a l o g e n a t e d compounds f i n d e x t e n s i v e commercial use as flame r e t a r d a n t s , (3.) and these are o f t e n used i n c o n j u n c t i o n w i t h ' s y n e r g i s t s ' , such as antimony t r i o x i d e or phosphorus d e r i v a t i v e s (J_). However, h a l o g e n - c o n t a i n i n g polymers g e n e r a l l y e v o l v e l a r g e amounts of smoke and c o r r o s i v e gases d u r i n g combustion, and t h e r e i s a g r e a t demand f o r n o v e l smoke-suppressant formulations. Polyester resins. The f i r e - p e r f o r m a n c e c h a r a c t e r i s t i c s o f u n s a t u r a t e d p o l y e s t e r r e s i n s are o f utmost importance i n many a p p l i c a t i o n a r e a s , p a r t i c u l a r l y i n the c o n s t r u c t i o n , t r a n s p o r t a t i o n and e l e c t r o n i c s i n d u s t r i e s (J_3). C o n s e q u e n t l y , these p l a s t i c s r e p r e s e n t one o f the major growth a r e a s f o r f i r e r e t a r d a n t s i n r e c e n t y e a r s (J_4).



oxide)

'paste'

8-stannic a c i d (hydrous t i n ( I V )

acid-

tin(IV)

3-stannic

Colloidal

stannate

Zinc

2

2

.xH 0 2

2

ZnSnO^

ZnSn(OH), 0

SnO

2

Sn0 .xH 0

2

Sn0 .xH 0

41.5*

51.1**

white powder

19.7

white powder

25% aqueous dispersion

51.3

70.3

white powder 73% d i s p e r s i o n in a phthalate plasticiser

78.8

white powder

(Reproduced with permission from Ref. 34, Copyright 1989 John Wiley & Sons Ltd.)

* Z i n c c o n t e n t = 22.8% * * Z i n c c o n t e n t = 28.2%

hydroxystannate

Zinc

oxide

Sn0

oxide

Anhydrous t i n ( I V )

2

Formula

Additive

Data on T i n A d d i t i v e s

Tin Content(%)

Physical

Physical State

Table I I .

3.9

3-3

1.3

-

5.2

6.9

Specific Gravity

2

ca. 1

ca. 1

0.03

ca.

ca.

2

Average Particle (Um) 0.3


Size

14.

CUSACK & KILLMEYER


193


E a r l i e r s t u d i e s a t the ITRI have demonstrated the e f f e c t i v e n e s s o f t i n ( I V ) o x i d e , both i n i t s anhydrous and hydrous forms, as a f l a m e - and smoke-retardant a d d i t i v e f o r l a b o r a t o r y - p r e p a r e d p o l y e s t e r r e s i n f o r m u l a t i o n s (J_5). In a r e c e n t study, c a r r i e d out i n c o l l a b o r a t i o n w i t h a major U.K. company, a number o f i n o r g a n i c t i n a d d i t i v e s have been i n c o r p o r a t e d i n t o a commercial brominated polyester resin. A l t h o u g h t h i s r e s i n , which c o n t a i n s 28% by weight bromine, i s i n t r i n s i c a l l y f l a m e - r e t a r d a n t , g i v i n g samples w i t h an 01 o f c a . 41 and which meet the UL94-VO c l a s s i f i c a t i o n , f o r m u l a t i o n s w i t h improved flame and smoke p r o p e r t i e s a r e sought. Antimony t r i o x i d e , 3 - s t a n n i c a c i d (hydrous t i n ( I V ) o x i d e ) , z i n c h y d r o x y s t a n n a t e , and z i n c s t a n n a t e were i n c o r p o r a t e d i n t o the commercial brominated p o l y e s t e r r e s i n a t l e v e l s o f 1,2,5 and 10% by weight. No p r o c e s s i n g problems were e n c o u n t e r e d and the samples c u r e d s a t i s f a c t o r i l y t o g i v e r i g i d , opaque s t r i p s . The i n c o r p o r a t i o n o f Sb^O^ i n t o the p o l y e s t e r l e a d s t o an i n t e r e s t i n g f l a m m a b i l i t y e f f e c t : a p r o g r e s s i v e i n c r e a s e i n 01 i s o b s e r v e d up t o an a d d i t i v e l e v e l o f 2%, above which the 01 d e c r e a s e s d r a m a t i c a l l y ( F i g u r e 1). I t has p r e v i o u s l y been r e p o r t e d (16,17) t h a t the optimum atomic r a t i o o f h a l o g e n : antimony i n s y n e r g i s t i c f l a m e - r e t a r d a n t systems appears t o depend upon the n a t u r e o f the h o s t polymer, and may o f t e n be f a r g r e a t e r than the s t o i c h i o m e t r i c p r o p o r t i o n s ( v i z . 3*1). Indeed, the 01 o f p o l y p r o p y l e n e c o n t a i n i n g a c h l o r i n a t e d h y d r o c a r b o n p a s s e s t h r o u g h a v e r y s h a r p maximum, w i t h i n c r e a s i n g Sb 0 , a t a Cl:Sb r a t i o o f c a . 25:1 (J_8). In the brominated p o l y e s t e r , the Br:Sb atomic r a t i o f o r optimum flame r e t a r d a n c y a l s o appears t o be about 25:1. Of the t i n a d d i t i v e s s t u d i e d , the anhydrous and h y d r a t e d z i n c s t a n n a t e s , ZnSnO and ZnSn(OH), r e s p e c t i v e l y , a r e c o n s i d e r a b l y more e f f e c t i v e f l a m e - r e t a r d a n t s y n e r g i s t s w i t h the bromine p r e s e n t i n the p l a s t i c than 3 - s t a n n i c a c i d ( F i g u r e 1). In l i n e w i t h t h i s o b s e r v a t i o n , o x i d i c t i n - z i n c systems have p r e v i o u s l y been found to e x h i b i t s u p e r i o r f l a m e - r e t a r d a n t p r o p e r t i e s t o t i n o x i d e s a l o n e (1922). In a d d i t i o n , ZnSnO g i v e s h i g h e r v a l u e s o f 01 than S b 0 a t a l l i n c o r p o r a t i o n l e v e l s s t u a i e d , and, i n f a c t , the 1% ZnSnO - c o n t a i n i n g p l a s t i c s o u t p e r f o r m samples c o n t a i n i n g 2% S b 0 ~ . I t i s i n t e r e s t i n g to note t h a t 3 - s t a n n i c a c i d i s s i g n i f i c a n t l y more e f f e c t i v e as a flame r e t a r d a n t than anhydrous S n 0 a t low a d d i t i v e l e v e l s ( F i g u r e 2) as p r e v i o u s l y r e p o r t e d i n a number o f h a l o g e n - c o n t a i n i n g polymer systems (15,22,23). In t h i s c o n n e c t i o n , thermal a n a l y s i s s t u d i e s of ABS-decabromobiphenyl-tin(IV) oxide systems have shown t h a t v e r y l i t t l e t i n ( I V ) bromide or t i n ( I V ) oxybromide i s v o l a t i l i s e d when anhydrous S n 0 i s used, but, i f the t i n i s p r e s e n t as 3 - s t a n n i c a c i d , and i f the atomic r a t i o o f Br:Sn i s h i g h e r than s t o i c h i o m e t r i c ( v i z . 4:1), then s i g n i f i c a n t v o l a t i l i s a t i o n o c c u r s , g i v i n g r i s e t o a vapour-phase f l a m e - r e t a r d a n t a c t i o n (23). T h i s d i f f e r e n c e i n r e a c t i v i t y between the two forms o f t i n ( I V ) o x i d e may be due t o the d i f f e r e n c e i n the s u r f a c e a r e a s o f t h e s e m a t e r i a l s : d e s p i t e b e i n g a c o a r s e r powder i n terms o f i t s average p a r t i c l e s i z e ( T a b l e I I ) , hydrous SnO has a s u r f a c e a r e a o f a t l e a s t an o r d e r o f magnitude g r e a t e r than t h a t o f the anhydrous m a t e r i a l (24). The advantage o f u s i n g a p a s t e d i s p e r s i o n o f a f l a m e - r e t a r d a n t a d d i t i v e i n t h i s p o l y e s t e r r e s i n f o r m u l a t i o n i s e v i d e n t from the 2

2

2

2



FIRE AND POLYMERS

0.1.

40-1 0

1

1

2

1

1

1

4 Additive

1

1

6

1

8

1

r10

(%)

F i g u r e 1. R e l a t i o n s h i p between the f l a m m a b i l i t y and metal compound l e v e l o f brominated p o l y e s t e r r e s i n samples. (Reproduced w i t h p e r m i s s i o n from Ref.3 *, C o p y r i g h t 1989 John Wiley & Sons L t d . ) 1



14.

CUSACK & KILLMEYER

195


m

°*

• 2%

(hyd)

(hyd) 'paste'

Sn0

2

F i g u r e 2. E f f e c t o f i n c o r p o r a t i o n l e v e l o f t i n o x i d e a d d i t i v e s on t h e f l a m m a b i l i t y o f brominated p o l y e s t e r r e s i n .



196

FIRE AND POLYMERS

d a t a shown i n F i g u r e 2. At i n c o r p o r a t i o n l e v e l s o f 2% and 5%, a d i s p e r s i o n o f 3 - s t a n n i c a c i d i n a p h t h a l a t e p l a s t i c i s e r ( s u p p l i e d by C h i n g h a l l L i m i t e d , M i l t o n Keynes, U.K.), g i v e s a s i g n i f i c a n t l y improved f l a m e - r e t a r d a n t performance over t h a t o f powdered 3 - s t a n n i c a c i d , presumably because o f i t s more u n i f o r m d i s t r i b u t i o n i n the polymer m a t r i x . A f u r t h e r improvement i n f l a m e - r e t a r d a n t e f f i c i e n c y i s observed when a c o l l o i d a l d i s p e r s i o n o f t i n ( I V ) o x i d e i s i n c o r p o r a t e d i n t o the p o l y e s t e r . At a 1.5% a d d i t i o n l e v e l , c o l l o i d a l SnO^ g i v e s an 01 v a l u e (49.0) which i s markedly h i g h e r than t h a t o b t a i n e d w i t h 5% l o a d i n g s o f e i t h e r anhydrous SnO (47.7) or 3 - s t a n n i c a c i d (47.9), as powdered a d d i t i v e s ( F i g u r e 2 ) . In a d d i t i o n t o i t s i n c r e a s e d f l a m e - r e t a r d a n t a b i l i t y , c o l l o i d a l S n 0 o f f e r s the f u r t h e r advantages o f t r a n s l u c e n c y i n the cured p l a s t i c , ease o f i n c o r p o r a t i o n and nons e t t l i n g i n the r e s i n p r i o r t o c u r e . E v a l u a t i o n o f the smoke g e n e r a t e d d u r i n g f l a m i n g combustion o f the brominated p o l y e s t e r r e s i n s has been c a r r i e d out i n an NBS Smoke Chamber. The d a t a o b t a i n e d , i l l u s t r a t e d g r a p h i c a l l y i n F i g u r e 3 and summarised i n T a b l e I I I , c l e a r l y i n d i c a t e t h a t both z i n c h y d r o x y s t a n n a t e and z i n c s t a n n a t e , when i n c o r p o r a t e d a t l e v e l s o f 2% or 5%, s i g n i f i c a n t l y reduce both the t o t a l amount and the r a t e o f p r o d u c t i o n , o f smoke e v o l v e d from the b u r n i n g brominated r e s i n . Although 3 - s t a n n i c a c i d and antimony t r i o x i d e have a s l i g h t b e n e f i c i a l e f f e c t on the r a t e o f smoke e m i s s i o n , n e i t h e r a d d i t i v e d e c r e a s e s the maximum o p t i c a l d e n s i t y o f the smoke, s a t u r a t i o n l e v e l s b e i n g reached i n each c a s e . Furthermore, ZnSn(OH). and ZnSnO are found t o be h i g h l y e f f e c t i v e as CO s u p p r e s s a n t s i n the r e s i n , when a s s e s s e d i n a n o v e l t e s t assembly c o m p r i s i n g the NBS Smoke Chamber i n c o n j u n c t i o n w i t h the c o n t i n u o u s CO monitor ( F i g u r e 4 and T a b l e I I I ) . S u b s t a n t i a l r e d u c t i o n s i n CO l e v e l s produced from z i n c s t a n n a t e - c o n t a i n i n g samples i n the NBS Smoke Chamber are e v i d e n t a t 3 minutes a f t e r i g n i t i o n and these e f f e c t s c o n t i n u e throughout the t e s t s , so t h a t maximum l e v e l s o f CO, a f t e r 10 minutes b u r n i n g , are a l s o much lower than f o r the base p l a s t i c . Antimony t r i o x i d e and B - s t a n n i c a c i d , a l t h o u g h showing some CO-suppressing a b i l i t y , a r e c o n s i d e r a b l y l e s s e f f e c t i v e i n t h i s r e s p e c t than e i t h e r ZnSn(OH)^ or ZnSnO (Table I I I ) . Hence, the z i n c s t a n n a t e s have been shown t o impart b e n e f i c i a l p r o p e r t i e s t o t h i s polymer system, i n terms o f f l a m m a b i l i t y and smoke/carbon monoxide e v o l u t i o n , and the improvements i n performance are c l e a r l y s u p e r i o r t o those e x h i b i t e d by the c o m m e r c i a l l y a v a i l a b l e antimony t r i o x i d e . 2

Other Halogenated Systems. I n o r g a n i c t i n compounds have been found t o e x h i b i t f l a m e - r e t a r d a n t and smoke-suppressant p r o p e r t i e s i n a number o f h a l o g e n - c o n t a i n i n g s y n t h e t i c polymer c o m p o s i t i o n s . In p a r t i c u l a r , T o u v a l (22) r e p o r t e d t h a t hydrous t i n ( I V ) o x i d e i s a t l e a s t as e f f e c t i v e as antimony t r i o x i d e when i n c o r p o r a t e d as a f l a m e - r e t a r d a n t s y n e r g i s t w i t h c h l o r i n e - c o n t a i n i n g compounds i n v a r i o u s t h e r m o p l a s t i c s i n c l u d i n g p o l y e t h y l e n e , p o l y p r o p y l e n e and a c r y l o n i t r i l e - b u t a d i e n e - s t y r e n e (ABS p l a s t i c ) . S i m i l a r l y , Fukatsu (25) demonstrated the f l a m e - r e t a r d a n t s u p e r i o r i t y o f hydrous S n 0 over S b 0 , a t l e v e l s o f 0.5% - 3%, i n a p o l y ( v i n y l a l c o h o l ) - p o l y ( v i n y l c h l o r i d e ) blended f a b r i c . Recent s t u d i e s a t I.T.R.I., c a r r i e d out i n c o l l a b o r a t i o n w i t h 2

2



CUSACK & K I L L M E Y E R


D,

Time (min.) F i g u r e 3E f f e c t o f i n o r g a n i c a d d i t i v e s on the d e n s i t y o f the smoke e v o l v e d from brominated p o l y e s t e r r e s i n i n the NBS-type Smoke Chamber. (Reproduced w i t h p e r m i s s i o n from Ref.34, C o p y r i g h t 1989 John Wiley & Sons L t d . )


Nelson; Fire and Polymers ACS Symposium Series; American Chemical Society: Washington, DC, 1990. A d d i t i v e s on t h e F i r e P r o p e r t i e s o f Brominated P o l y e s t e r R e s i n

0%

1000

46.2

n

949


a t end o f e x p e r i m e n t , i . e . 10 m i n u t e s a f t e r

61.1%

54.5%

24.0%

13.8%

i g n i t i o n o f sample.

866

1013

7.5

-

**Measurements r e c o r d e d

00

i g n i t i o n o f sample.

32.8%

672

56.1

1690

1917

37.5%

1390

2587

2813

4967

4783

56.5%

52.7%

16.5%

19.6%

38.7%

44.5%

3300 3645

8.2% 5463

18.0% 50.6%

-

1100

-

n

1825

3.5

3.0

-

4.0

3 minutes a f t e r

37.1%

629

56.0

CO

CO

881

850

GO

0 0

* Measurements r e c o r d e d

6

ZnSn0

"

3

ZnSn(OH)

"

2

S n 0 ( h y d ) 47.9

3

"

2

5% S b 0 10.1%

26.3%

737

54.2

899

29.8%

702

53.4

ZnSn0

"

6

ZnSn(0H)

"

3

12.1%

3

879

2

S n 0 ( h y d ) 45.1

"

2

51.2

-

41.2

Sb 0

2%

n

Smoke D e n s i t y

CO E v o l u t i o n (ppm) Red Time(min)to A c t u a l ( 3 m i n ) * R e d ( 3 m i n s ) Max.** (max). D (3min)* R e d * ( 3 m i n ) D_(max) D = s s CO 5950 2225 1000 3.0 00 4700 21.0% 1650 4.0 25.8% 851 14.9%

of Inorganic

None

Flammability 01

Effect

Additive

Table I I I .




[CO]


p.p.m.

Time

(min.)

F i g u r e 4. E f f e c t o f i n o r g a n i c a d d i t i v e s on t h e e m i s s i o n o f carbon monoxide from brominated p o l y e s t e r r e s i n i n t h e NBS-type Smoke Chamber. (Reproduced w i t h p e r m i s s i o n from R e f . 3 4 , C o p y r i g h t 1 9 8 9 John Wiley & Sons L t d . )


200

FIRE AND POLYMERS


e x t e r n a l o r g a n i s a t i o n s , have shown t h a t c e r t a i n i n o r g a n i c t i n a d d i t i v e s , i n c l u d i n g SnO^, ZnSnCOH)^ and ZnSnO , are e f f e c t i v e f l a m e and s m o k e - r e t a r d a n t s i n a range o f c h l o r i n a t e d polymers, i n c l u d i n g r i g i d PVC, (26) f l e x i b l e PVC and neoprene. Hence, i t i s apparent t h a t c e r t a i n i n o r g a n i c t i n compounds are v e r y e f f e c t i v e flame r e t a r d a n t s and smoke s u p p r e s s a n t s f o r h a l o g e n a t e d polymer f o r m u l a t i o n s . S i n c e t h e s e a d d i t i v e s are g e n e r a l l y n o n - t o x i c , t h e i r p o t e n t i a l use as p a r t i a l or t o t a l r e p l a c e m e n t s f o r e x i s t i n g commercial flame r e t a r d a n t s , such as antimony t r i o x i d e , i s thought t o m e r i t s e r i o u s c o n s i d e r a t i o n . HALOGEN-FREE POLYMER SYSTEMS In r e c e n t y e a r s , t h e r e has been i n c r e a s i n g c o n c e r n about the t o x i c i t y and c o r r o s i v e n a t u r e o f the smoke and gases g e n e r a t e d d u r i n g the combustion o f h a l o g e n - c o n t a i n i n g polymers (27). Consequently, t h e r e i s a c o n s i d e r a b l e demand f o r p l a s t i c s which comply t o the s p e c i f i c a t i o n 'low smoke zero h a l o g e n (LSOH) flame r e t a r d a n c y , p a r t i c u l a r l y f o r use i n underground t r a n s p o r t , s h i p p i n g and power stations. As a r e s u l t , t h e r e has been much i n t e r e s t i n the use o f n o n - t o x i c i n o r g a n i c a d d i t i v e s and f i l l e r s , and the market f o r t h e s e compounds i s l i k e l y to c o n t i n u e i t s r a p i d growth i n the y e a r s ahead (28). 1

E t h y l e n e - a c r y l i c Rubber. The use o f PVC as a w i r e and c a b l e i n s u l a t i o n m a t e r i a l has d e c l i n e d i n r e c e n t y e a r s , and i t has been r e p l a c e d to a s i g n i f i c a n t e x t e n t by h a l o g e n - f r e e e l a s t o m e r i c compositions. At the p r e s e n t time, such f o r m u l a t i o n s a r e made f l a m e - r e t a r d a n t by the i n c o r p o r a t i o n o f a l u m i n a t r i h y d r a t e (ATH). A l t h o u g h ATH i s e s s e n t i a l l y n o n - t o x i c and r e l a t i v e l y inexpensive, h i g h a d d i t i o n l e v e l s are n e c e s s a r y f o r e f f e c t i v e n e s s , and t h i s o f t e n r e s u l t s i n a marked d e t e r i o r a t i o n i n the m e c h a n i c a l p r o p e r t i e s o f the polymer (29). While r e c e n t advances i n p r o d u c t i o n t e c h n o l o g y and s u r f a c e c o a t i n g have m i t i g a t e d some o f the problems a s s o c i a t e d w i t h h i g h f i l l e r l o a d i n g , (29) improved systems c o m p r i s i n g c o m b i n a t i o n s o f ATH w i t h o t h e r a d d i t i v e s are under i n v e s t i g a t i o n . A c o l l a b o r a t i o n has been u n d e r t a k e n w i t h the A d m i r a l t y Research Establishment, Poole, U.K., i n which the f i r e - r e t a r d a n t p r o p e r t i e s o f a number o f i n o r g a n i c t i n compounds i n a non-halogenated, ATHf i l l e d e t h y l e n e - a c r y l i c rubber f o r m u l a t i o n , are b e i n g a s s e s s e d . P r e l i m i n a r y r e s u l t s have i n d i c a t e d t h a t a marked flame-retardant s y n e r g i s m e x i s t s between c e r t a i n t i n compounds ( a t a 2.5% l e v e l ) and ATH (50% l o a d i n g ) , and an i n c r e a s e i n 01 from 27.5 ( f o r no t i n a d d i t i v e ) t o 33.0 was observed f o r the ZnSn(OH)^ c o n t a i n i n g formulations. I t has been r e p o r t e d (30_) t h a t an ATH l o a d i n g o f 60% i s n e c e s s a r y to r a i s e the 01 o f e t h y l e n e - a c r y l i c rubber t o a v a l u e o f 33, and t h a t such a f o r m u l a t i o n meets the MOD Naval S p e c i f i c a t i o n NES 518. Hence, i t appears t h a t lower t o t a l a d d i t i v e l e v e l s are r e q u i r e d f o r adequate performance when ATH - ZnSn(OH)^ c o m b i n a t i o n s are used than when ATH i s i n c o r p o r a t e d a l o n e . This s i g n i f i c a n t r e d u c t i o n i n the f i l l e r c o n t e n t may prove advantageous i n terms o f the m e c h a n i c a l p r o p e r t i e s o f the p o l y m e r i c s u b s t r a t e . E l e v a t e d temperature 01 d a t a ( F i g u r e 5) i n d i c a t e t h a t the t i n c o n t a i n i n g e l a s t o m e r s r e t a i n t h e i r f l a m e - r e t a r d a n t s u p e r i o r i t y up to a temperature o f 250°C above which the samples undergo e x t e n s i v e



14.


201


F i g u r e 5. E f f e c t o f temperature on the f l a m m a b i l i t y e t h y l e n e - a c r y l i c rubber samples.


of

202

FIRE AND POLYMERS 1

t h e r m a l d e g r a d a t i o n and d e t e r m i n a t i o n o f 0 1 s becomes i m p r a c t i c a l . I t i s o f i n t e r e s t t o note t h a t the polymer c o n t a i n i n g ZnSn(OH)^ does not burn i n a i r even a t 250°C and, a c c o r d i n g l y , t h i s c o m p o s i t i o n has a temperature index o f a t l e a s t 50°C above t h a t o f the rubber c o n t a i n i n g ATH a l o n e . The 01 and h i g h temperature 01 d a t a t h e r e f o r e p r o v i d e s u b s t a n t i a l e v i d e n c e as t o the b e n e f i t o f u s i n g ZnSn(OH)^ as a f l a m e - r e t a r d a n t s y n e r g i s t w i t h alumina t r i h y d r a t e f i l l e r . Other Non-halogenated Systems. Although o x i d i c t i n compounds, i n c l u d i n g hydrous S n 0 and ZnSn(OH)., can impart a h i g h degree o f f l a m e - r e s i s t a n c e t o c e l l u l o s i c s u b s t r a t e s , such as c o t t o n f a b r i c (19) and paper, they are g e n e r a l l y i n e f f e c t i v e as flame r e t a r d a n t s i n h a l o g e n - f r e e s y n t h e t i c polymer f o r m u l a t i o n s , u n l e s s the c o m p o s i t i o n has a r e l a t i v e l y h i g h i n o r g a n i c f i l l e r c o n t e n t . However, t h e s e t i n a d d i t i v e s can e x h i b i t s i g n i f i c a n t smokes u p p r e s s a n t p r o p e r t i e s i n non-halogenated polymers. In a programme of s t u d i e s c a r r i e d out a t ITRI i n c o l l a b o r a t i o n w i t h Borax Research L i m i t e d , C h e s s i n g t o n , U.K., a s e r i e s o f d i v a l e n t metal h y d r o x y s t a n n a t e s and s t a n n a t e s were s c r e e n e d as smoke s u p p r e s s a n t s i n h a l o g e n - f r e e g l a s s - r e i n f o r c e d p o l y e s t e r (GRP) p a n e l s ( 3 1 ) . The b e s t r e s u l t o b t a i n e d was f o r a 2phr ( p a r t s per hundred o f r e s i n ) i n c o r p o r a t i o n l e v e l o f ZnSnO , which gave a 46% r e d u c t i o n i n smoke d e n s i t y compared to the c o n t r o l sample.


2

Furthermore, H i r s c h l e r ( 3 2 ) has i n v e s t i g a t e d the smoke-reducing a b i l i t y o f a number o f metal h y d r o x i d e s and o x i d e s , a t i n c o r p o r a t i o n l e v e l s o f up t o 40 phr i n a c r y l o n i t r i l e - b u t a d i e n e - s t y r e n e (ABS) copolymer. At the lowest a d d i t i v e l e v e l s t u d i e d (10 p h r ) , SnO gave a h i g h e r degree o f smoke suppressancy ( v i z . 58%), than any o f the o t h e r compounds, and l o a d i n g s o f a t l e a s t 30 phr were found t o be n e c e s s a r y t o a c h i e v e comparable performance w i t h e i t h e r A1(0H) or Mg(0H) 5

Tne e f f e c t i v e n e s s o f i n o r g a n i c t i n compounds as flame and smoke r e t a r d a n t s , both a l o n e and i n c o m b i n a t i o n w i t h i n o r g a n i c f i l l e r s , i n s e v e r a l h a l o g e n - f r e e t h e r m o p l a s t i c , t h e r m o s e t t i n g and e l a s t o m e r i c s u b s t r a t e s , i s c u r r e n t l y under i n v e s t i g a t i o n a t the ITRI. MECHANISTIC STUDIES A l t h o u g h t h e r e have been many s t u d i e s on the mode o f a c t i o n o f f i r e r e t a r d a n t s g e n e r a l l y , (J_6) the m e c h a n i s t i c b e h a v i o u r o f t i n a d d i t i v e s i s l e s s c l e a r , and may depend on s e v e r a l f a c t o r s i n c l u d i n g the r a t i o of h a l o g e n : t i n i n the system. Thermal a n a l y s i s has been used e x t e n s i v e l y t o study i n d e t a i l the v a r i o u s i n d i v i d u a l s t a g e s o c c u r r i n g d u r i n g the breakdown o f polymers under the a c t i o n o f heat, and can p r o v i d e u s e f u l i n f o r m a t i o n r e g a r d i n g the mode o f a c t i o n and the e f f e c t i v e n e s s o f f l a m e - r e t a r d a n t additives. Simultaneous thermogravimetry (TG), d i f f e r e n t i a l thermogravimetry (DTG) and d i f f e r e n t i a l t h e r m a l a n a l y s i s (DTA), have been used a t the ITRI t o i n v e s t i g a t e the t h e r m a l breakdown o f v a r i o u s t i n - c o n t a i n i n g polymers and o f the a d d i t i v e s t h e m s e l v e s . Simultaneous TG/DTA s t u d i e s o f z i n c h y d r o x y s t a n n a t e ( F i g u r e 6 ) , i n d i c a t e t h a t d e h y d r a t i o n o f t h i s compound o c c u r s d u r i n g the temperature range 190°-285°C, w i t h a l o s s o f 19.1% o f i t s i n i t i a l weight, t h i s c o r r e s p o n d i n g t o the l o s s o f 3 moles o f water:




Weight

1 0


(%)

1

1 200

1

1 400

Temp.

1

1 600

1

1— 800

(°C)

F i g u r e 6. Simultaneous TG/DTA t r a c e s o f z i n c h y d r o x y s t a n n a t e in a i r . (Reproduced w i t h p e r m i s s i o n from R e f . 3 4 , C o p y r i g h t 1 9 8 9 John Wiley & Sons L t d . )


204

FIRE AND POLYMERS ZnSn(OH). o

•

ZnSnCL 3

+

3H 0 2 o

T h i s t h e r m a l d e h y d r a t i o n i s accompanied by a l a r g e endotherm ( a b s o r p t i o n o f h e a t ) , as p r e v i o u s l y r e p o r t e d (J_2). A secondary p r o c e s s o c c u r s a t h i g h e r temperatures (ca_. 580°-800°C), accompanied by a broad exotherm, due t o a s o l i d s t a t e r e a c t i o n i n which no weight l o s s i s o b s e r v e d : (12)


ZnSnO^

i

•

Zn SnO^ 2

+

J Sn0

2

E x t e n s i v e t h e r m o a n a l y t i c a l s t u d i e s have been c a r r i e d out on the brominated p o l y e s t e r r e s i n system. F i g u r e 7 shows the d i f f e r e n c e s i n the t h e r m a l breakdown b e h a v i o u r o f the 2% ZnSnO - c o n t a i n i n g p o l y e s t e r , when the atmosphere i s a i r as opposed t o argon. Although t h e r e a r e s l i g h t d i f f e r e n c e s i n the i n i t i a l d e c o m p o s i t i o n s t a g e s , the most s i g n i f i c a n t d i s s i m i l a r i t y o c c u r s a t h i g h e r temperature where, i n a i r , a t h i r d d i s t i n c t weight l o s s o c c u r s . T h i s l o s s i s accompanied by a l a r g e exotherm, i n d i c a t i v e o f an o x i d a t i v e 'burnoff of r e s i d u a l char. The r e a c t i o n s o f the polymer i n a i r a r e o b v i o u s l y more r e l e v a n t to i t s f l a m m a b i l i t y than those i n argon, and thermal a n a l y s i s d a t a f o r brominated p o l y e s t e r samples i n a i r , a r e p r e s e n t e d i n T a b l e IV. In the absence o f any i n o r g a n i c a d d i t i v e , the r e s i n l o s e s about 80% of i t s weight d u r i n g the i n i t i a l d e c o m p o s i t i o n s t a g e , t h i s c o r r e s p o n d i n g t o the l o s s o f s t y r e n e and HBr, (33) f o l l o w e d by char o x i d a t i o n (13-7% l o s s ) a t a DTG max (temperature o f maximum r a t e o f weight l o s s ) o f c a . 528°C. I n c o r p o r a t i o n o f a 2% l e v e l o f e i t h e r ZnSn(OH)^ or ZnSnO into the r e s i n , l e a d s t o marked d i f f e r e n c e s i n i t s t h e r m a l d e g r a d a t i o n profile. The i n i t i a l d e c o m p o s i t i o n comprises two d i s t i n c t s t a g e s , the major s t e p o c c u r r i n g a t a lower temperature than t h a t o f the u n t r e a t e d polymer, which may be i n d i c a t i v e o f promotion o f bromine v o l a t i l i s a t i o n by the z i n c s t a n n a t e s . Furthermore, the amount o f r e s i d u e b u r n t o f f i n the char o x i d a t i o n s t e p i s g r e a t l y i n c r e a s e d i n the t i n - c o n t a i n i n g samples, and the temperature a t which t h i s p r o c e s s o c c u r s i s s i g n i f i c a n t l y h i g h e r than i n the base r e s i n . Hence, the t i n a d d i t i v e s may a l s o be a c t i n g as condensed phase char promotors. In c o n t r a s t t o t h e s e o b s e r v a t i o n s , a 2% a d d i t i o n o f °3 the polymer r e s u l t s i n o n l y a s l i g h t change i n i t s t h e r m a l d e c o m p o s i t i o n , w i t h o n l y a modest i n c r e a s e i n char r e s i d u e , which i s , i n t u r n , b u r n t o f f a t a s l i g h t l y h i g h e r temperature than t h a t o f the c o r r e s p o n d i n g s t a g e i n the u n t r e a t e d r e s i n ( T a b l e I V ) . These findings indicate that S ^ ^ condensed phase f i r e r e t a r d a n t a c t i v i t y i n t h i s p o l y e s t e r system, and t h i s i s i n a g r e e ment w i t h the g e n e r a l l y a c c e p t e d o b s e r v a t i o n t h a t antimony a d d i t i v e s o p e r a t e p r i m a r i l y i n the vapour phase by i n t e r f e r i n g w i t h the f r e e r a d i c a l r e a c t i o n s a s s o c i a t e d w i t h combustion p r o c e s s e s ( 1 , 1 6 ) . Continuous m o n i t o r i n g o f the c a r b o n monoxide and carbon d i o x i d e e v o l v e d d u r i n g t h e r m a l d e c o m p o s i t i o n o f brominated p o l y e s t e r r e s i n samples, has been c a r r i e d out u s i n g a s i m u l t a n e o u s t h e r m a l a n a l y s i s mass s p e c t r o m e t r y t e c h n i q u e . In o r d e r t o a l l o w measurement o f the c a r b o n monoxide e v o l v e d , the atmosphere chosen f o r t h e s e runs was 21% oxygen i n argon, s i n c e the peak a t 28 atomic mass u n i t s (amu) S b

t

2

0

n

a

s

l

i

t

t

l

e


o

14.

CUSACK & KILLMEYER


Weight

205


(%)

AIR

Temp. (°C) F i g u r e 7. Simultaneous TG/DTA t r a c e s o f brominated p o l y e s t e r r e s i n c o n t a i n i n g 2% ZnSnO i n a i r and i n a r g o n . (Reproduced w i t h p e r m i s s i o n from R e f . 3 4 , C o p y r i g h t 1989 John Wiley & Sons L t d . )

due t o n i t r o g e n (N^) i n a i r , would have o b s c u r e d the CO peak, a l s o a t 28 amu. CO^ was monitored a t 44 amu. The r e s u l t s o b t a i n e d ( T a b l e V) c l e a r l y show t h a t the p r e s e n c e o f 5% B - s t a n n i c a c i d i n the r e s i n s u b s t a n t i a l l y reduces both the t o t a l amounts o f , and the r a t e s o f e v o l u t i o n o f , CO and CO^, produced d u r i n g t h e r m a l d e g r a d a t i o n o f the p l a s t i c .



78.5

50.5 13.9 372.3

337.3 406.2

: c a . 180-450°C

: c a . 450-650°C

++Temp. range

Atmosphere: a i r Flow r a t e : 20cm /min H e a t i n g r a t e : 10°C/min

+ Temp, range

* Experimental c o n d i t i o n s :

2% S b ^

J

414.3

15.7

2 % ZnSnO

332.1

48.4

361.6

Degradation* DTG max

2 % ZnSn(OH).

Initial Loss (%) (°C)

18.5

34.1

35.5

13-7

Weight

Data f o r Brominated P o l y e s t e r

80.7

Weight

Thermal A n a l y s i s

No a d d i t i v e

Sample

T a b l e IV.

Samples*

558.4

578.0

572.5

527.9

Char O x i d a t i o n * * Loss (%) DTG max

Resin


(°C)

14. CUSACK & KILLMEYER


207

T a b l e V. A n a l y s i s o f Gases E v o l v e d D u r i n g Thermal D e g r a d a t i o n o f Brominated P o l y e s t e r R e s i n Samples Sample -

No a d d i t i v e 5% S n 0 ( h y d )


2

„ . ^. „ . ** S p e c i f i c Emission Carbon Monoxide Carbon D i o x i d e 1+ Total Total 1+ II++ II++ 146 211 78 65 375 453 262 18 232 88 70 30

ft Atmosphere : 21% oxygen i n a r g o n ; h e a t i n g r a t e = 2 0 ° C / m i n . *» I n t e g r a t e d gaseous p r o d u c t i o n , n o r m a l i s e d f o r i n i t i a l sample weight ( a r b i t r a r y u n i t s ) . F i r s t major d e c o m p o s i t i o n s t a g e ( c a . 3 5 0 - 3 7 0 ° C ) .

+

Second major d e c o m p o s i t i o n s t a g e

(ca.

540-560°C).

F u r t h e r i n s i g h t i n t o the mode o f a c t i o n o f the i n d i v i d u a l a d d i t i v e s i s p r o v i d e d by s i m p l e combustion e x p e r i m e n t s , c a r r i e d o u t in air. T a b l e VI shows t h a t the y i e l d o f i n v o l a t i l e carbonaceous c h a r , formed when brominated p o l y e s t e r i s burned t o c o m p l e t i o n , i s more than doubled when brominated p o l y e s t e r i s burned t o c o m p l e t i o n , i s more than doubled when 5% a d d i t i o n s o f e i t h e r 3 - s t a n n i c a c i d o r z i n c s t a n n a t e a r e made t o the p l a s t i c , t h i s o b s e r v a t i o n b e i n g c o n s i s t e n t w i t h condensed phase b e h a v i o u r . Elemental a n a l y s i s o f the r e s i d u e s s u g g e s t s t h a t , a l t h o u g h i n the case o f 3 - s t a n n i c a c i d , o n l y a s m a l l f r a c t i o n o f the t i n i s v o l a t i l i s e d , a v e r y s i g n i f i c a n t p r o p o r t i o n o f both the z i n c and the t i n i s v o l a t i l i s e d from the z i n c s t a n n a t e - c o n t a i n i n g polymer, which may be i n d i c a t i v e o f vapour phase action. I n t e r e s t i n g l y , the e x t e n t o f bromine l o s s i s s i g n i f i c a n t l y reduced f o r t i n - c o n t a i n i n g samples, p a r t i c u l a r l y those c o n t a i n i n g ZnSnO . Antimony t r i o x i d e , which undergoes almost complete v o l a t i l i s a t i o n i n the polymer, shows l i t t l e char e n c h a n c i n g b e h a v i o u r and o p e r a t e s p r i m a r i l y i n the gas phase. The a p p a r e n t a b i l i t y o f z i n c s t a n n a t e t o a c t i n both the condensed and vapour phases may account f o r i t s o v e r a l l f l a m e - r e t a r d a n t s u p e r i o r i t y t o the o t h e r inorganic additives studied.

CONCLUSIONS 1.

2.

Z i n c h y d r o x y s t a n n a t e and z i n c s t a n n a t e are v e r y e f f e c t i v e f l a m e r e t a r d a n t s y n e r g i s t s when i n c o r p o r a t e d a t l e v e l s o f 1-10% i n t o a brominated p o l y e s t e r r e s i n , and a r e , i n g e n e r a l , markedly superior to other inorganic a d d i t i v e s studied i n c l u d i n g , antimony t r i o x i d e , anhydrous t i n ( I V ) o x i d e , and 3 - s t a n n i c a c i d . The s u r f a c e a r e a and degree o f d i s p e r s i o n i n the polymer m a t r i x o f the f i r e - r e t a r d a n t a d d i t i v e has a pronounced e f f e c t on i t s efficiency. C o l l o i d a l t i n ( I V ) o x i d e i s s i g n i f i c a n t l y more e f f e c t i v e , i n terms o f i t s f l a m e - r e t a r d a n t a b i l i t y , than powdered t i n ( I V ) o x i d e o r 3 - s t a n n i c a c i d .



element; bromine

itself

94.4

34.3

93.0

-

Sb

+

(1,16).

vapour

condensed vapour

condensed

-

Primary Phase of A c t i o n *

from Brominated

i n the vapour phase

(%)

a c t s almost e x c l u s i v e l y

-

42.9

18.4

-

Elemental V o l a t i l i s a t i o n Sn Zn


*With r e g a r d t o m e t a l l i c

3

33.5

2

5%

Sb 0

52.8

5% ZnSnO^ 74.0

85.1

53.0

Sn0 (hyd)

5%

2

95.9

24.1

additive

Br

No

(%)

Char Y i e l d

R e s i d u a l Char Y i e l d s and E x t e n t s o f E l e m e n t a l V o l a t i l i s a t i o n P o l y e s t e r R e s i n Samples d u r i n g Combustion i n A i r

Sample

T a b l e VI.


14. 3.


4.

5.

6.

7.

CUSACK & KILLMEYER


209

ZnSnCOH)^ and ZnSnO , a t l e v e l s o f 2% or 5%, s i g n i f i c a n t l y d e c r e a s e both the t o t a l amount and the r a t e o f p r o d u c t i o n , o f smoke and carbon monoxide g e n e r a t e d from brominated p o l y e s t e r r e s i n , when b u r n t under l i m i t i n g or f l a m i n g c o n d i t i o n s . Antimony t r i o x i d e and B - s t a n n i c a c i d o n l y e x h i b i t m a r g i n a l b e n e f i t s i n terms o f smoke and CO s u p p r e s s i o n i n t h i s polymer system. T h e r m o a n a l y t i c a l and r e l a t e d m e c h a n i s t i c s t u d i e s i n d i c a t e t h a t the t i n a d d i t i v e s a r e p r i m a r i l y condensed phase flame r e t a r d a n t s , and t h e s e can a l t e r the p y r o l y s i s o f h a l o g e n a t e d polymers by promoting the l o s s o f h a l o g e n and enhancing c r o s s - l i n k i n g , t o g i v e an i n c r e a s e i n the y i e l d o f t h e r m a l l y - s t a b l e carbonaceous c h a r , w i t h a concomitant d e c r e a s e i n the g e n e r a t i o n o f v o l a t i l e flammable p r o d u c t s . T h i s r e d u c t i o n i n the amount o f f u e l s u p p l i e d t o the flame l e a d s t o the o b s e r v e d s u p p r e s s i o n o f smoke and carbon monoxide. In a d d i t i o n , p a r t i a l v o l a t i l i s a t i o n of z i n c and t i n o c c u r s d u r i n g combustion o f brominated r e s i n s c o n t a i n i n g ZnSn(OH), or ZnSnO , and t h i s i n d i c a t e s t h a t t h e s e a d d i t i v e s may c o n t r i b u t e t o vapour phase flame r e t a r d a t i o n , which may account f o r t h e i r s u p e r i o r i t y t o t i n o x i d e i t s e l f , where the e x t e n t o f t i n v o l a t i l i s a t i o n i s v e r y low. Antimony t r i o x i d e has l i t t l e e f f e c t on the t h e r m a l breakdown o f the polymer and o p e r a t e s p r i m a r i l y i n the gas phase. C e r t a i n i n o r g a n i c t i n compounds a r e e f f e c t i v e f l a m e - r e t a r d a n t s y n e r g i s t s when i n c o r p o r a t e d a t a 2.5% l e v e l i n t o a 50% ATHf i l l e d e t h y l e n e - a c r y l i c rubber c o m p o s i t i o n . Tin-containing elastomer formulations r e t a i n t h e i r flame-retardant s u p e r i o r i t y at e n v i r o n m e n t a l temperatures up t o 250°C, and samples c o n t a i n i n g 2.5% ZnSn(OH)^ do not s u s t a i n combustion i n a i r a t t h i s temperature. In g e n e r a l , t i n compounds do not e x h i b i t f l a m e - r e t a r d a n t p r o p e r t i e s i n h a l o g e n - f r e e polymer systems, u n l e s s the composition contains a high inorganic f i l l e r loading. However, t i n a d d i t i v e s o f t e n a c t as smoke s u p p r e s s a n t s i n non-halogenated polymers. I n o r g a n i c t i n compounds, i n p a r t i c u l a r , z i n c h y d r o x y s t a n n a t e and z i n c s t a n n a t e , a r e e f f e c t i v e f i r e r e t a r d a n t s i n a number o f polymer systems. They appear t o have advantages over c e r t a i n e x i s t i n g commercial a d d i t i v e s , namely: (a) Non-toxicity (b) No d i s c o l o r a t i o n o f s u b s t r a t e (c) E f f e c t i v e a t low l e v e l s (d) L i t t l e apparent e f f e c t on m e c h a n i c a l p r o p e r t i e s (e) F l a m e - r e t a r d a n t s y n e r g i s m w i t h h a l o g e n s and/or alumina t r i h y d r a t e (f) Smoke s u p p r e s s i o n (g) Decrease i n c a r b o n monoxide p r o d u c t i o n (h) Wide range o f a p p l i c a b i l i t y

ACKNOWLEDGMENTS Messrs A.W.Monk and J.A.Pearce, and Miss S.J.Reynolds a r e g r a t e f u l l y acknowledged f o r e x p e r i m e n t a l a s s i s t a n c e . Miss J . R a t c l i f f e i s thanked f o r a s s i s t a n c e i n the d e s i g n o f F i g u r e s f o r t h i s paper.


210

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32. Hirschler,M.M. Polymer 1984, 25, 405. 33. Haines,P.J.; Lever,T.J.; Skinner,G.A. Thermochimica Acta 1982, 59, 331. 34. Cusack,P.A.; Monk,A.W.; Pearce,J.A.; Reynolds,S.J. Fire & Mater. 1989, 14, 23. RECEIVED January 17, 1990


Inorganic Tin Compounds as Flame, Smoke, and Carbon Monoxide

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